The subject of the invention is a switch for a MV or HV traction line test device comprising multiple pairs of contacts connected in series and controlled by separated multiple coils. The switch is able to reclose in a millisecond range and can operate in medium or high voltage systems which are characterized with high load impedance. Exemplary applications of the switch are the generation of short voltage pulses to the high impedance load or providing temporary galvanic insulation between a voltage sensor and a medium voltage source.

Requirements of the MV or HV mechanical switch for a traction line test device are challenging. On the one hand, a small current rating of the device enables utilization of small contacts with low inertia which could be fast. On the other hand, achieving high voltage withstand capability needs a wider isolation gap between the contacts. This implies slower operation of the switch.

Voltage withstand capability of the medium voltage switch (e.g. vacuum interrupter) is obtained by providing a sufficient gap between the switch contacts. A typical medium voltage switch is designed in respect to the possibility of the occurrence of relatively large short-circuit currents and electrodynamic forces, and therefore contacts of MV switches are large and heavy with relatively large inertia and operation of the switch is relatively slow (>15ms).

The control of all switching elements (opening and closing) must be done simultaneously with a tolerance of typically less than a millisecond, since the total voltage across the switch cascade would otherwise be unevenly distributed to their individual elements and it could lead to overvoltage of individual semiconductor switching elements and thus to their destruction.

In order to provide millisecond range reclosing operation of the switch large, costly and complicated actuator system are used (eg. a Thomson drive).

Such medium voltage switches are not optimized for applications with high impedance of the load. In systems where the load is characterized with high impedance, smaller contacts shall be used. However, a sufficient gap between the contacts is still needed to provide sufficient voltage withstand capability.

The known solution of that problem is to replace a single pair of the contacts and a single large gap with several pairs of contacts with smaller gaps connected in series. This solution increases the voltage withstand capability of the switch. However, it is characterized by a complicated mechanical actuator system which must provide simultaneous reclosing operation of all pairs of the switch contacts and provide proper galvanic insulation between them.

In case that each pair of contacts is controlled by a separate coil, galvanic separation between the coils is needed.

Moreover, the total voltage across the medium or high voltage switch should be evenly distributed between cascaded pairs of contacts. The total voltage rating of the switch should be n x V_{BR contact/contact}, where n is number of pairs of contacts connected in the cascade and V_{BR contact/contact} is the breakdown voltage between contacts of a pair of contacts.

Rated voltage between contacts and driving coil of the pairs of contacts is limited and it equals V_{BR contact/coil}. Due to this fact, driving coils of cascaded pairs of contacts cannot be connected to the same potential and also cannot be connected to the ground. Otherwise, electric potential from the first coil in the cascade will be same as the last coil and the total voltage rating of the cascade will be only 2 x V_{BR contact/coil} regardless of the number of the pairs of contacts in series. Therefore an isolated power supply for relay control coils is needed.

German patent DE102014002298 relates to a device for galvanically isolated transmission of control signals for a cascaded high voltage switch. The device for electrically isolated transmission of the control signals has at least one primary winding connectable to a drive circuit for the high voltage switch and a plurality of secondary windings connectable to the semiconductor switching elements of the high voltage switch and which are arranged magnetically coupled to the primary winding. The primary and secondary windings are formed as conductor tracks on or in one or more printed circuit boards and are penetrated by the magnetic field of a single magnetic core, which is arranged on or in the circuit boards. The proposed device is thus a common planar transformer for the isolated driving of all or at least some of the switching elements of a cascaded high-voltage switch. This planar transformer has only one magnetic core for all windings arranged on or in the planar transformer. In principle, several of those planar transformers can be used for the control of a cascaded high-voltage switch, each of the planar transformer then controls a group of switching elements. Document EP 0 555 946 A2 discloses a traction line testing device with a plurality of pairs of contacts.

The object of the present invention is to provide a new construction of the MV or HV switch having high voltage rating of the switch and providing proper galvanic insulation of the control coils which does not have the above-mentioned problems and can be produced inexpensively and reproducibly in terms of electrical properties.

The object is achieved with the device according to claim 1.

According to the claimed invention, a switch for medium or high voltage traction line testing device comprises a plurality of normally-opened pairs of contacts connected in series wherein each pair of contacts is equipped with a separate control coil. The switch further comprises a wireless power transfer supply module being on ground potential for supplying cascaded wireless power transfer receivers comprising a transmitting coil, a high frequency inverter and a microcontroller, and a plurality of cascaded wireless power transfer receivers for supplying a control coil of the pairs of contacts. Each of the wireless power transfer receiver is referenced to the floating potential and comprises a receiving coil. Each of control coils is connected to one of the wireless power transfer receivers. Furthermore, the receiving coils of the wireless power transfer receivers are magnetically coupled. Furthermore, a wireless power transfer supply module is located in the middle of the cascaded wireless power transfer receivers.

Advantageous embodiments of the device are the subject of the dependent claims or can be found in the following description and the embodiment.

The switch, preferably, further comprises blocking diodes connected in series with pairs of contacts.

Preferably the switch consists of a plurality of modules, each module comprising pairs of contacts, a control coil, a wireless power transfer receiver and a blocking diode. The blocking diode shall be rated for the same voltage as a pair of contacts.

In addition the switch further comprises balancing capacitors arranged in parallel to each of the pairs of contacts and/or comprises balancing capacitor arranged in parallel to the blocking diodes so that even voltage distribution between the wireless power transfer receivers can be obtained.

Preferably the switch comprises pairs of contacts which are made as vacuum reed relays.

The switch preferably comprises balancing resistors placed in parallel to each of pairs of contacts so that equal sharing of DC component can be obtained. The resistance of balancing resistors is one range lower than the DC resistance of the pairs of contacts.

Preferably each of wireless power transfer receivers of the switch comprises an additional capacitor energy bank. Preferably the capacitor energy bank is in the form of a ceramic SMD capacitor.

Preferably each of wireless power transfer receivers is equipped with a one-way communication link with the wireless power transfer supply module for sending a signal about closing of the relays.

Each of wireless power transfer receivers preferably comprises also an electronic rectifier and triggering circuit for the control coil.

Wireless power transfer receivers are manufactured as PCB's.

The high frequency inverter of the wireless power transfer supply module preferably works with a frequency in the range 100-300 kHz. The inverter is responsible for the excitation of the transmitting coil.

The pairs of contacts have preferably a meandering arrangement, preferably with a layer of silicon resin between each of the pairs of contacts. This significantly improves the volume utilization, and the proper isolation between the pairs of contacts.

Coils of the switch are supplied by a cascaded inductive power transfer circuit comprising a plurality of cascaded wireless power transfer receivers providing galvanic insulation between the particular coils. It allows also to achieve sufficient isolation between coils and from the coils to ground.

Utilization of the wireless power transfer (WPT) technology for driving coils of the pairs of contacts eg. mechanical relays, allows to increase voltage capabilities of the switch and provide proper galvanic isolation between the coils.

The switch is scalable. WPT technology has relatively high efficiency, which means that large number of pairs of contacts may be connected in series. It can be extended for higher voltages (HV) and high current circuit breakers like Vacuum Interrupters.

The construction of the switch according to the invention does not contain any magnetic cores, which makes the switch cost efficient.

The proposed switch will be explained in more detail using an exemplary embodiment in conjunction with the drawings. The invention is shown by means of example embodiments on a drawing, in which:

• Fig.1 Schematic diagram of the proposed switch.
• Fig.2 Model of the single vacuum reed relay with capacitor.
• Fig.3 Schematic diagram of the module of the proposed switch.
• Fig.4 Model of the proposed switch having meandering arrangement of pairs of contacts.

A proposed switch 1 for a medium or high voltage traction line testing device comprises a plurality of normally-opened pairs of contacts 2, in the form of vacuum reed relays, connected in series wherein each pair of contacts 2 is equipped with a separate control coil 3. Dimensions of the pairs of contacts 2 Z are limited in order to reduce its inertia. Individual pair of contacts 2 close when the respective control coil 3 is supplied.

The switch 1 comprises also a wireless power transfer supply module 4 which is on ground potential and is used for supplying cascaded wireless power transfer receivers 5. Wireless power transfer supply module 4 is in the form of a transmitting board and comprises a transmitting coil, a high frequency inverter and a microcontroller. The high frequency inverter works with frequency in the range 100-300 kHz. The inverter is responsible for the excitation of the transmitting coil.

Furthermore the switch 1 comprises a plurality of cascaded wireless power transfer receivers 5 for supplying the control coil of the pairs of contacts. Each of the wireless power transfer receivers 5 is referenced to the floating potential and comprises receiving coil 6, which are magnetically coupled.

Each of control coils 3 is connected to one of the wireless power transfer receivers 5 and is supplied from the energy which is harvested by the receiving coil 6 of the wireless power transfer receiver 5.

The switch 1 further comprises balancing capacitors 8 which are arranged in parallel to each of the pairs of contacts 2 and/or comprises balancing capacitors 9 arranged in parallel to blocking diodes 7 so that even voltage distribution between wireless power transfer receiver is obtained. The blocking diode 7 is rated for same voltage as a pair of contacts 2.

It further comprises balancing resistors 10 placed in parallel to each of pairs of contacts 2 wherein the resistance of the balancing resistors 10 is one range lower than the DC resistance of the pairs of contacts 2.

Wireless power transfer receivers 6 are manufactured as PCB's and further comprise an electronic rectifier and triggering circuit for the control coil 3. Wireless power transfer receivers 5 comprise additionally a capacitor energy bank, preferably in the form of ceramic SMD capacitors.

Wireless power transfer receivers 5 are also equipped with a one-way communication link with the wireless power transfer supply module 4 for sending signal about closing of the relays.

In another preferred embodiment of the proposed switch 1 the pairs of contacts 2 have meandering arrangement, preferably with a layer of silicon resin between each of the pairs of contacts 2. It significantly improves the volume utilization. A layer of silicon resin provides proper isolation.

In yet another preferred embodiment of the proposed switch, said switch comprises several modules, wherein each module comprises a pair of contacts 2, a control coil 3, a wireless power transfer receiver 5 and a blocking diode 7. The modules allow for easy expansion of the switch 1, which makes the solution scalable and allows the switch 1 to be adjusted to the assumed voltage.